1. Field of the Invention
The present invention relates to a manufacturing method of a film-like material made of a resin, more particularly, to a manufacturing method of a film-like material made of a thermoplastic resin with excellent appearance. The invention also relates to a crystalline thermoplastic resin film with a high elastic modulus and a high strength and a manufacturing method of the same.
Conventionally the following methods have been known as a manufacturing method of a film made of a thermoplastic resin; a T-die molding method for extruding a melted resin into a thin film-like shape out of a slit die with a wide width, so-called T-die and an inflation molding method for molding a cylindrical film by extruding a resin into a cylindrical shape out of a die slit of such as a ring die and the like while cooling the resin and keeping it flat by two plates. Also, a calendar molding method (Japanese Provisional Publication No. 10-296766(A)) using a plurality of calendar rolls has been known.
However, the above-described methods have the following problems.    (1) If a resin with a high molecular weight, a resin with a high melt viscosity, or a resin deficient in melt elongation is used, defects such as voids are easy to be formed and the appearance of the film becomes inferior and especially in the case of production of a film with a film thickness of 200 μm, the appearance was considerably inferior.    (2) In the case of the above-described calendar molding method, when melted resin composition is passed through a pair of calendar rolls while forming a bank, the molding is carried out while making the peripheral velocities of both heated rolls different, so that the surface of the obtained film is not necessarily smooth and beautiful and the surface inevitably becomes roughened and also from such a point, subsequently, it is impossible to produce a film with a sufficiently high film thickness precision.    (3) In the case of the T-die molding method and the inflation molding method, the film thickness precision of the molded film is insufficient and especially, in the case of producing a film from a resin with a high melt viscosity and a hardly formable resin with a low melt elongation degree, the film thickness precision is significantly deteriorated and these methods cannot be said a proper molding method as a manufacturing method of a film or a sheet required to provide a high film thickness precision.
The invention has been developed taking the above-described circumferences into consideration and a object of the invention is to provide a manufacturing method capable of obtaining a film-like material made of resin and having excellent appearance.
In consideration of the above-described problems of the conventional techniques, another object of the invention is to provide a method for producing a film-like material made of a resin and having a high film thickness precision even in the case of using a resin material with a high melt viscosity and a low melt elongation degree, for example, a thermoplastic resin containing a long molecular chain polyolefin.
As a film of a crystalline thermoplastic resin, various kinds of films have been known and employed for practical uses. As a technology of providing a crystalline thermoplastic resin film with a high elastic modulus, for example, Japanese Patent Application Laid-Open No. 7-173302 discloses a manufacturing method of a polypropylene sheet using a polypropylene mixed with a crystallization nucleating agent.
Although the polypropylene sheet produced by the above-described known technique is provided with a higher elastic modulus than that of polypropylene sheets produced ever before and improved secondary processibility such as the vacuum molding property, these improvements cannot be said sufficient yet.
The other purpose of the invention is to provide a crystalline thermoplastic resin film with a high elastic modulus and a high strength and a manufacturing method for the same.
2. Description of the Related Art